1. Field of the Invention
The present invention relates to a method for generating animation. In this method, frames containing images are classified as key frames or intermediate frames. This method can be used to automate intermediate dividing in animation creation, such as the techniques known as "inbetweening" or "tweening". The present invention also relates to recording media for storing a program for the above method and to an animation transmission/receiving system using this method.
2. Description of the Prior Art
Much of the modern world has only been made possible because of developments in techniques for communicating visual images. Visual images have grown, along with audio, to play a central role in today's information and entertainment culture. The increasing demand for images in a variety of forms has promoted development of imaging-related techniques and resulted in the creation of a global "video culture". The field of animation is a clear example. Improved video quality and the introduction of computer graphics (hereinafter "CG") has made it possible for generators to express refined and complicated images and works of art that would have remained forever trapped within the imaginations of their predecessors.
In NTSC, one of the currently common television standards, thirty frames per second (30 FPS) are generally displayed; a simplified display method called limited animation requires fifteen frames per second (15 FPS); while for motion pictures, twenty-four frames (24 FPS) is most common. The current situation requires a number of pictures no less than fifteen times the length of the animation in seconds in order to create animation. An hour long animation requires an enormous number of pictures, numbering in the tens of thousands.
In order to achieve more efficient picture production, an intermediate dividing method has been known where one animator first draws important frames called key frames and other animators then cooperate to draw the frames in between (hereinafter "intermediate frames"). The efficiency of this method is, however, still restricted because the pictures are hand drawn.
Recently, this intermediate dividing method has been applied to CG animation programs. In such programs, object movements are allotted according to a time axis. A key frame is allotted to a moment when an event occurs. An animation in which a nail is hammered may, for example, require two key frames, one showing a hammer flung up and another showing the hammer as it has just hit the nail. After being drawn, the key frames are first input into a computer. The positions of the object between the two key frames are then calculated for intermediate dividing.
The easiest applicable calculation is linear interpolation. With linear interpolation, an object is shown moving between two frames at a constant speed. Recently, other methods called ease-in (acceleration) and ease-out (deceleration) have also been put into practice to cope with object which do not move at a constant speed between key frames. Still further, a technique for generating natural and smooth intermediate frames has become available for expressing an object's moving path with a spline line.
Japanese Patent Laid-open No. Sho 60-191366 discloses a conventional general intermediate dividing technique. According to this invention, when a character on key frames consists of a plurality of curves, its shape on intermediate frames is created through calculation after a user manually designates correspondence of the respective curves between a plurality of key frames.